1. Field of the Invention
The present invention relates to a comparator and more particularly to a comparator having a hysteresis characteristic.
2. Description of the Prior Art
A comparator having two input terminals has its output determined depending upon a mutual relation between the input voltages applied to the respective input terminals. Such comparator is applied to an input section of a digital circuit, and it operates in such manner that it compares the input signals applied to the respective input terminals and generates an output when predetermined one of the input signals is higher than the other or when the predetermined one is lower than the other. This operation is for the purpose of waveform shaping or noise elimination of the input signals. However, mere comparison of the input signals with each other does not attain a sufficient noise elimination effect. A comparator having a hysteresis characteristic enhances a noise elimination rate by operating in such manner that an output is generated when predetermined one of input signals is higher than the other input signal by a predetermined voltage and the output is inverted when the one input signal becomes lower than the other input signal by another predetermined voltage. The comparator with a hysteresis characteristic still has the following drawbacks. Since a feedback circuit is coupled to one of the input terminals, the hysteresis characteristic is affected by the input signal applied across the input terminals. Moreover, the conventional comparator with a hysteresis characteristic is not suited to a monolithic integrated circuit device, because the feedback circuit sometimes has a resistor of a value which is hard to be realized in a semiconductor chip.